Make sure your stomach is full when you go grocery shopping. Shopping with empty stomach will end you up buying the things that are not on your list and will lead you over your budget. Because you feel hungry you tend to grab the unnecessary things that you think will fill up your stomach instead of your pantry.
This trick really works with me and my husband. One time we went grocery shopping and he is really hungry, he grabs as much food as he can, which end up sitting on our fridge for days. I told him never go shopping when your hungry. He then try to shop when he is full and he then told me "you are right, I did not grab too much food this time" in fact he did not even want to buy any snack because he is full.